The mechanisms by which platelets respond to physiological stimuli will be investigated, with emphasis on 1) the role of calcium as a primary cellular regulatory agent 2) the adjustment in energy metabolism following stimulation, and 3) the regulation of glycogen phosphorylase. BIBLIOGRAPHIC REFERENCES: Chaiken, R., Pagano, D., and Detwiler, T. C., Regulation of Platelet Phosphorylase, Biochim. Biophys. Acta, 403, 315-325 (1975). Detwiler, T. C., Martin, B. M. and Feinman, R. D. Stimulus-Response coupling in the thrombin-platelet interaction, Biochemistry and Pharmacology of Platelets, Ciba Foundation Symposium 35(new series). pp 77-91 (1975).